The present invention relates generally to computer input devices, and particularly to computer input devices (e.g., a mouse or trackball) employing a ball which is rotated and tracked to provide control signals to a computer system. More specifically, the invention concerns the generation of ordered patterns for application to the spherical surface of such a ball, which enable movement of the ball to be reliably tracked by known optical tracking engines.
A traditional computer input device, such as a mouse, includes a housing with a ball mounted in the housing. In the well known computer mouse, the ball mount is configured such that the ball engages a work surface and rotates based upon the user""s movement of the mouse across a work surface. Alternatively, the ball may be mounted within a trackball device, and rotated by a user""s direct digital manipulation. In either case, most conventionally, rotary optical-mechanical position encoders are used to detect rotation of the ball in its mount, and to provide position information indicative of that rotation to an associated computer. In most instances, the position information is used to control movement of a visual image (such as a cursor) on the display screen of the computer.
More recently, direct optical tracking of a ball has been proposed for a cursor control device, as a desirable alternative to conventional optical-mechanical encoder-type tracking devices. For example, Sato U.S. Pat. No. 5,027,115 discloses a pen-type computer input device having a ball with a golf ball-like pattern of lands and recesses. Photosensors arrayed along X and Y axes detect the lands and recesses as they move, thereby detecting the distance traversed by the ball. A similar arrangement is disclosed in Xerox Disclosure Journal Vol. 10, No. 3 May/June 1985. A ball similar in appearance to a golf ball is marked with a feature pattern comprising a uniform pattern of light dots on a dark background or a uniform pattern of dark dots on a light background, or alternatively golf ball-like dimples. An LED light source illuminates a ball pattern area and a sensor detects a series of patterns produced from rotation of the ball; the series of patterns are used to determine the amount and direction of ball movement.
A problem has been found to arise with attempts to optically track a regular or uniform ball surface patterns such as those disclosed in the aforementioned references. In particular, attempts to track such regular patterns, with known tracking engines, can give rise to aliasing effects resulting in associated cursor jump or skip. Aliasing arises due to an inability of the processing means to effectively discriminate between successive ball pattern surface area images received by the optical sensing means.
Bidiville et al. U.S. Pat. No. 5,703,356 discloses a cursor control device utilizing a ball with its surface covered with a plurality of randomly shaped markings, providing an overall effect of a randomly speckled ball. A pattern area is illuminated with a monochromatic light source, and a sensor having an array of photosensitive elements receives an image reflected from the pattern area. xe2x80x9cBiologically inspiredxe2x80x9d circuitry associated with the sensor determines movement of the pattern across the array, and translates the movement into conventional control signals supplied to a host system. Bidiville et al""s use of a random, irregularly patterned ball surface pattern addresses the aliasing problem that can arise with attempts to track a regular ball surface pattern. Through use of surface pattern irregularity, successive xe2x80x9csnapshotsxe2x80x9d of the ball surface pattern detected by the sensor may be distinguished from each other by the processing means, thereby avoiding aliasing induced jump or skip of the cursor.
While seemingly effective in avoiding aliasing related tracking problems, the Bidiville et al. ball patterns are necessarily irregular and random in appearance; regular patterns are excluded. This may be undesirable from an aesthetic or industrial design perspective. A design architecture permitting generation of a variety of regular ordered patterns that do not, when tracked, induce adverse aliasing effects, would be highly desirable. It would permit greater artistic freedom in the design of aesthetically pleasing ball patterns, and at the same time enable reliable tracking of the ball by known optical tracking engines.
In a first aspect, the invention provides a method of creating an ordered surface pattern to be applied to a ball of a computer input device. In accordance with the invention, an individual ball pattern design element is selected and replicated to create a plurality of like design elements. The like design elements are arranged in predetermined relation to a grid pattern established in relation to a sub-element of the ball""s spherical surface. The sub-element is defined as one of three radially symmetrical sub-elements obtained by dividing the ball""s spherical surface into octants and subdividing one of the octants. The grid pattern includes first and second sets of intersecting grid lines.
In a second related aspect, the invention provides a method of providing a ball for use in a computer input device with an optically trackable spherical surface, by printing on the ball""s spherical surface an ordered surface pattern area having the unique characteristics just described.
In a third related aspect, the invention provides a ball for use in a computer input device. The ball has a spherical surface bearing an ordered surface pattern having the unique characteristics just described, for permitting movement of the ball to be optically tracked.
The above and other features and advantages of the present invention will be readily apparent and fully understood from the following detailed description of preferred embodiments, taken in connection with the appended drawings.